Describe how an equal-arm balance is made and how it works

Two pans of equal weight are suspended from the beam, one at each end, at the fulcrum (a type of lever). A pointer on the right angles to the beam and leaver indicates zero on a scale when the beam is at rest, parallel  to a level surface.

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Wish i can but don’t know this

You would be correct, boiling water does disinfect contamination.    the property of disinfecting means to kill  germs, bacteria and other pathogens or contamination  that might cause an infection or cause a person to become sickly. a couple methods of disinfecting are using soap, other cleaning supplies or by simply "boiling" the contaminate.  the reason why boiling water disinfects certain attributes is because some cells cannot survive the heat and pressure.